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       <title>Hydra User Reference</title>
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    The Hydra user reference is divided into categories where each category corresponds to one of the
    components a Hydra job. Each category has is a summary page that provides a description
    of the category and a list of each item in the category. The list of
    items includes a brief description for each item.
    <p>The approximate status of the documentation writing for each category is:
    <table width="50%">
        <tr>
            <th style="text-align:left">Category</th>
            <th style="text-align:left">Description</th>
        </tr>
        <tr><td>&nbsp;</td></tr>
        <tr>
            <td><a href="com/addthis/hydra/task/run/TaskRunnable.html">Hydra Jobs</a></td>
            <td>top-level specification of the Hydra jobs</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/task/source/TaskDataSource.html">Input Sources</a></td>
            <td>input to a job</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/data/filter/bundle/BundleFilter.html">Bundle Filters</a></td>
            <td>transformations that accept a bundle as input</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/data/filter/value/AbstractValueFilter.html">Value Filters</a></td>
            <td>transformation that accept a value as input</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/task/output/TaskDataOutput.html">Output Sinks</a></td>
            <td>output from a job</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/task/output/tree/PathElement.html">Path Elements</a></td>
            <td>describe the nodes in tree output</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/data/tree/TreeDataParameters.html">Data Attachments</a></td>
            <td>additional information that is attached to tree nodes</td>
        </tr>
        <tr>
            <td><a href="com/addthis/hydra/data/query/QueryOp.html">Query Operations</a></td>
            <td>query operations that are performed on tree output</td>
        </tr>
    </table>
    <p>Most Hydra jobs are specified using one of the forms listed in the "Hydra Jobs" category.
    This would be a good place to start if you have just started reading this reference guide.
    The most common types of Hydra jobs, split jobs and map jobs, are both specified using the
    <code>'type : "<a href="com/addthis/hydra/task/map/StreamMapper.html">map</a>"'</code> specification.

    <p>Each documentation page should include a summary of the item, one or more examples illustrating
    how to use that item in a job specification, and a description for each field of the item.
    If you have any questions, comments, additions, or suggestions for the documentation
    please submit it on IRC on #hydra at freenode.net or <a href="http://github.com/addthis/hydra/issues">github</a>.</p>
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